Project Summary/Abstract. It is not clear why some individuals with allergen-specific IgE suffer from allergies, while others do not. It is likely that multiple factors contribute, including differences in IgE affinity or epitope diversity for allergens, mast cell numbers, Fc?RI expression levels, Syk signaling, allergen-specific IgG antibodies, and anti-IgE antibodies. An addition factor that has not been considered is the contribution of glycosylation to IgE. Our long-term goal is to understand how glycosylation of antibodies regulates, and is regulated, by immune responses. Our central hypothesis is that IgE effector function is regulated differentially by defined glycans at distinct positions. Indeed, this is supported by preliminary data shown in this application. The rationale that underlies the proposed research is that understanding the contribution of specific IgE glycans to allergic inflammation will enable new and innovative allergic therapies. We will test our central hypothesis and, thereby, attain the objective of this application by pursuing the following three specific aims: 1) Define the IgE glycan requirements for Fc?RI binding; 2) Determine how sialic acid regulates IgE-mediated anaphylaxis; 3) Examine the regulation of IgE glycosylation in vivo. Using an approach that combines biophysics, cellular and molecular immunology, and glycobiology, we will determine glycans a essential for IgE-Fc?RI interactions, define a novel anti-anaphylactic pathway, establish pathogenic IgE glycosylation patterns, and attenuate anaphylaxis by modulating IgE glycans. In addition to enabling discovery of biomarkers marking allergy-causing IgE, the studies here will potentially result in identification of novel therapeutic targets for allergic disease. Finally, these studies will have impact beyond allergy in diseases in which IgE is involved, including systemic lupus erythematosus (SLE) and helminth infection. !